Osteoporotic fractures associated with low bone mineral density (BMD) are a significant public health problem for women, resulting in over 1 million fractures per year. The increasing incidence of fractures will make an already major health problem an even greater one in the future. Estimates of medical costs for the treatment of osteoporotic fractures are expected to increase from $14.8 billion in 1995 to $60 billion by 2020. Although the Women's Health Initiative is investigating dietary and hormonal factors in relation to bone density, it is not investigating the effects of exercise on reducing bone mineral loss in postmenopausal women.
This study includes completion of a large, partially randomized clinical trial evaluating the effect of a 1-year exercise intervention on total body and regional BMD in two populations (hormone replacement therapy [HRT] versus no HRT) of postmenopausal women with a previous history of physical inactivity. A major hypothesis is that, compared to the no-exercise group, the exercise intervention will be an effective alternative to reduce the risk of osteoporosis and the exercise effects will be larger in the cohort of women on HRT than those not on HRT.
The exercise program includes progressive resistance exercises using free weights and weight resistance machines and weight-bearing aerobic exercises. We carefully supervise and monitor the exercise compliance by keeping records of the amount of exercise completed at each of three weekly exercise sessions and by measuring strength gains of selected muscle groups. We will measure biochemical markers of bone formation and resorption and hormonal correlates of bone mineral density changes including sex steroids at baseline, 6 months, and 1 year.
We have obtained duplicate blood collections, made one week apart, for all cohorts at each of the three measurement periods. We have also collected duplicate dual energy x-ray absorptiometry (DXA) scans at each time period to follow changes in axial and appendicular BMD and total and regional soft tissue body composition as a result of the intervention. We collected extensive dietary intake records during the first year of intervention; we will monitor dietary intake in a 2-year followup using food frequency questionnaires. We will also measure followup BMD, soft tissue, and lean and fat body composition for 2 years in all women who complete the first-year intervention program.
Two-hundred sixty-six women have completed the first year of the intervention. The study has a retention rate of 92 percent in the first year for the first four cohorts.
Because of the paucity of information regarding long-term effects of exercise, and because of the increased emphasis in the scientific community on evaluating the long-term efficacy of exercise interventions for osteoporosis prevention, this comprehensive 1-year clinical trial and 2-year followup will make an important contribution to determining the future role of combining progressive resistance and weight bearing aerobic exercise in the prevention of osteoporosis in two populations (HRT vs. no HRT) of postmenopausal women.
Purpose
